The present invention relates to a flow dividing valve. More specifically, the invention relates to a flow dividing valve capable of freely setting the ratio of flow rates for dividing the fluid in an inlet port into a plurality of outlet ports.
A flow dividing valve is capable of dividing the fluid in an inlet port into a plurality of outlet ports at a predetermined ratio of flow rates irrespective of the pressures in the outlet ports. This enables, accordingly, a stable flow rate to be fed to the hydraulic actuators in a plurality of systems by using a single oil hydraulic pump, making it possible to simplify the circuit and to decrease the cost of the apparatus. This flow dividing valve is used for actuating an operation apparatus equipped with hydraulic actuators and for actuating an attachment fitted to the operation apparatus in, for example, a construction machine by the fluid discharged from a single hydraulic pump.
With reference to FIG. 3, the flow dividing valve generally designated at a numeral 20 includes a flow rate control spool 24 inserted in a valve body 22, and a needle 26 provided in a flow passage communicated with an inlet port P of the valve body 22 to form a throttle. The flow rate control spool 24 is inserted in a spool slide hole 22a formed in the valve body 22 to freely slide therein, and is pushed, by a compression spring 25 arranged on one end side (left end side in FIG. 3) of the low rate control spool 24, against the side of the other end thereof. The spool slide hole 22a communicates with the inlet port P, an outlet port A and an outlet port B. Part of the fluid in the inlet port P flows into the outlet port B through the needle 26 and the flow rate control spool 24, and the remainder thereof flows into the outlet port A through the flow rate control spool 24. Due to the throttle effect, there is produced a pressure difference between the upstream side of the needle 26 and the downstream side thereof. The pressure on the downstream side is guided to an end where the compression spring 25 of the flow rate control spool 24 is arranged, and the pressure on the upstream side is guided to the other end of the flow rate control spool 24. The needle 26 is attached to the valve body 22 via its external thread 26a. The extent (opening degree) of the throttle is controlled by adjusting the screw-in amount of the needle 26. The needle 26 that has been adjusted for its screw-in amount is secured by a lock nut 26b. 
The flow rate control spool 24 slides in the spool slide hole 22a due to a pressure difference between the upstream side and the downstream side, which is determined by the opening degree of the needle 26, whereby the openings to the outlet port A and to the outlet port B are adjusted and accordingly, the flow is adjusted and divided. When the pressures change in the outlet port A and in the outlet port B, the flow rates to these ports through the flow rate control spool 24 undergo a change depending on a change in the pressure difference before and after passing through the flow rate control spool 24. Consequently, the flow rate of the fluid flowing into the needle 26 changes to cause a change in the pressure difference between the upstream side and the downstream side of the needle 26. According to this change in the difference in the pressure, the flow rate control spool 24 so slides as to maintain a predetermined ratio of flow rates despite of changes in the pressures in the outlet port A and in the outlet port B. Accordingly, the ratio of flow rates in the outlet port A and in the outlet port B is determined by the throttle opening degree of the needle 26.
The above-mentioned conventional flow dividing valve involves the following problem that must be solved. That is, the ratio of flow rates is manually set by adjusting the opening degree of the needle, making it difficult to instantaneously and arbitrarily accomplish the setting in accordance with the operating amount of the operation lever as desired by an operator. It has therefore been desired to provide a flow dividing valve capable of instantaneously changing the ratio of flow rates.
The present invention has been accomplished in view of the above-mentioned fact, and its technical subject is to provide a flow dividing valve which enables the ratio of flow rates to be instantaneously and continuously set so that the fluid in the inlet port can be divided at a predetermined ratio of flow rates to a plurality of outlet ports.
In order to solve the above-mentioned technical problem according to the present invention, there is provided a flow dividing valve for dividing the fluid in an inlet port into a plurality of outlet ports irrespective of the pressures in the outlet ports, comprising:
a flow rate control spool for dividing the flow rate of the fluid in said inlet port into a predetermined ratio of flow rates, and
a flow rate ratio-setting spool for setting said ratio of flow rates to control said flow rate control spool, said flow rate ratio-setting spool being operated by a control signal from an external unit.
The ratio of flow rates is set by operating, by means of a control signal, the flow rate ratio-setting spool that controls the flow rate control spool.
In a preferred embodiment, the ratio of flow rates can be continuously set to an arbitrary value. A pilot hydraulic pressure is used as said control signal. The flow rate ratio-setting spool is provided with a variable throttle that is adjusted by said control signal.
The ratio of flow rates is instantaneously and continuously set to an arbitrary value by the control signal. The ratio of flow rates is instantaneously set in accordance with the magnitude of the pilot hydraulic pressure that is the control signal. Further, the ratio of flow rates is set depending on the throttle opening degree of the variable throttle that is adjusted by the control signal.